Towed electrified vehicle battery charging rate control

ABSTRACT

An electrified vehicle includes a human-machine interface to enable towed vehicle mode and specify a desired traction battery charge upon arrival at a destination. A controller is programmed to vary charging rate of the traction battery while the electrified vehicle is being towed over a user-specified distance to the destination to obtain the user-specified target charge for the traction battery upon reaching the destination. The target charge may be entered as a percentage state of charge (SOC), a distance to empty (DTE), or Watt hours, and converted to net energy input required for the traction battery. The controller distributes the charging load over the entire distance to reduce the affect on the drivability and efficiency of the towing vehicle by varying regenerative braking of the electric machine(s) while being towed to provide a net energy needed to obtain the target charge upon reaching the destination.

TECHNICAL FIELD

This disclosure relates to controlling an electrified vehicle inpreparation for being towed and while being towed by another vehicle.

BACKGROUND

Electrified vehicles may include drivetrains that use electric pumps forlubrication and thermal conditioning of the drivetrain and tractionbattery. Unlike a non-electrified vehicle that may include one or moremechanical pumps operated by movement of the vehicle, towing of anelectrified vehicle in the ignition off state or in a non-propulsionmode will not activate electric pumps, and towing an electrified vehiclein an ignition on state may result in certain undesirable conditions.

In addition, the user may want to add some charge to the HV tractionbattery of the electrified vehicle while it is being towed so that theelectrified vehicle has a specified state of charge (SOC) or travelrange (also referred to as distance to empty (DTE)) upon arrival at thedestination. The user usually knows the destination, but may not knowthe distance to the destination or the time required to reach thedestination by the towing vehicle (which may often be longer than thetime required when not towing a vehicle).

SUMMARY

A towed vehicle mode for an electrified vehicle may enable operation ofone or more electric pumps to provide lubrication and/or cooling ofvehicle components including one or more drivetrain components and thetraction battery while the vehicle is being towed. The towed vehiclemode may be selected using a vehicle HMI. Various driver controls,driver assistance features, and alerts may be disabled while in thetowed vehicle operating mode, such as automatic emergency braking,object detection, accelerator pedal position-based regenerative braking,lane departure alerts/steering, automatic parking brake operation,automatic gear selection, and similar features. Driver controls, such ascruise control, steering wheel, accelerator pedal, etc. may be disabledas a theft deterrent of the towed vehicle while stopped with the towedvehicle mode active. Low-voltage system support may be provided to powerthe pump(s) and maintain charge of an associated auxiliary battery usingthe traction battery and/or regenerative braking of the electrifiedwhile the towed vehicle mode is activated. Alerts specific to towedvehicle operation may be transmitted to an associated mobile wirelessdevice. Braking assistance may be provided using regenerative brakingand/or hydraulically actuated friction brakes based on brake activationof the towing vehicle or detection by vehicle speed, acceleration,and/or distance sensors/cameras without an electrical or wirelessconnection to the towing vehicle. Automatic braking of the towedelectrified vehicle may be performed to bring the vehicle to acontrolled stop if the vehicle detects disconnection from the towingvehicle. Tail lights and brake lights of the electrified vehicle may beactivated without an electrical connection or wireless connection to thetowing vehicle. Traction battery charge maintenance or a desired stateof charge (SOC) or distance to empty (DTE) upon arrival at thedestination may be specified by the user with regenerative energycapture of the towed electrified vehicle controlled to maintain orachieve the specified SOC or DTE. Traction battery charging rate may becontrolled to achieve the specified SOC or DTE to minimize the effect ontowing vehicle drivability and efficiency and overtaxing of the towingvehicle drivetrain and cooling systems.

In various embodiments, an electrified vehicle includes a drivetrainhaving an electric machine configured to provide propulsive torque tovehicle wheels, a high-voltage traction battery selectively connected tothe electric machine, and a controller programmed to, after receiving asignal enabling towed vehicle operation of the electrified vehicle, varycharging rate of the high-voltage traction battery while the electrifiedvehicle is being towed over a user-specified distance to a destinationto obtain a user-specified target charge for the high-voltage tractionbattery upon reaching the destination. The electrified vehicle mayinclude a human-machine interface (HMI) in communication with thecontroller, wherein the HMI receives the user-specified distance and theuser-specified target charge for the high-voltage traction battery, andgenerates the signal enabling towed vehicle operation in response toassociated input. The user-specified target charge may be received bythe HMI as a percentage state of charge (SOC) of the high-voltagetraction battery. The controller may be further programmed to vary thecharging rate based on net energy input to the high-voltage tractionbattery needed to obtain the user-specified target SOC. The controllermay vary the charging rate by varying power generated by the electricmachine based on the net energy needed to obtain the user-specifiedtarget SOC. The controller may be programmed to vary the power generatedby the electric machine based on a distance remaining to the destinationdivided by an average vehicle speed and a difference between the targetSOC and a current SOC of the high-voltage traction battery.

In some embodiments, the user-specified target charge may be received asa distance to empty (DTE) for the electrified vehicle via the HMI. Thecontroller may be further programmed to convert the DTE to acorresponding SOC. The controller may convert the DTE to thecorresponding SOC by retrieving the corresponding SOC from a lookuptable based on net energy input to the high-voltage traction batteryneeded to obtain the DTE. The controller may be further programmed tovary the charging rate by controlling non-braking regenerative power ofthe electric machine.

Embodiments may also include a method for controlling an electrifiedvehicle having a drivetrain including an electric machine configured toprovide propulsive torque to vehicle wheels and a traction battery,comprising, by a vehicle controller: receiving a signal to activatetowed vehicle operation and controlling charging rate of the tractionbattery while the electrified vehicle is being towed to distributecharging of the traction battery to a user-specified charge over auser-specified distance. The method may also include receiving theuser-specified charge and the user-specified distance via ahuman-machine interface (HMI) of the electrified vehicle after receivinginput to activate the towed vehicle operation from the HMI. The methodmay include receiving the user-specified charge as a percentage state ofcharge (SOC) for the traction battery after traveling the user-specifieddistance.

In one or more embodiments, the method may include receiving theuser-specified charge as a distance to empty (DTE) for the electrifiedvehicle via the HMI. The method may further include converting the DTEto a corresponding SOC for the traction battery. Converting the DTE to acorresponding SOC may include retrieving the corresponding SOC from alookup table based on net energy required to obtain the DTE. The methodmay include controlling the charging rate by charging the tractionbattery based on a net energy input required to achieve theuser-specified charge, the net energy input required being divided bytime required to travel the user-specified distance. The method may alsoinclude controlling non-braking regenerative power of the electricmachine to control the charging rate.

Embodiments may also include an electrified vehicle system having adrivetrain including an electric machine powered by a traction battery,a human-machine interface (HMI), and a controller programmed to, inresponse to an enabling signal received in response to input via theHMI, control charging rate of the traction battery to evenly distributecharging to a target charge input via the HMI over a distance input viathe HMI. The target charge may be received by the HMI as a percentagestate of charge (SOC) of the traction battery or a distance to empty(DTE). The controller may be further programmed to control regenerativeenergy capture of the electric machine while being towed to control thecharging rate based on net energy input to the traction battery requiredto obtain the target charge after being towed the distance input via theHMI.

One or more embodiments according to the disclosure may have associatedadvantages. For example, various embodiments facilitate flat towing ofan electrified vehicle, which generally requires less effort than atowing trailer/dolly to attach and disconnect, in addition toeliminating the weight of the trailer/dolly in the total system weight.The use of the towed vehicle brakes provides an effective way to helpstop the towed electrified vehicle, which may be required in somejurisdictions. Control of an electrified vehicle according to one ormore embodiments provides oil lubrication and/or cooling to thedrivetrain, supports the low-voltage system including a low-voltage (LV)auxiliary battery without drawing power from the towing vehicle, andmaintains or increases the high-voltage (HV) traction battery state ofcharge (SOC) or distance to empty (DTE) using regenerative braking at arate that minimizes the effect on the towing vehicle. In addition,control of the towed electrified vehicle maintains the vehicle in Drivegear with Drive gear operation producing no electric machine torqueunless HV battery charging is desired. Embodiments may also prevent thetowed electrified vehicle from shutting down due to low speed for aperiod of time, and prevent the towed electrified vehicle propulsionsystem from entering an active mode (including disabling various drivercontrols such as the accelerator pedal, steering wheel, gear selector,etc.) until a customer key or authentication device is present toprevent drive away theft. Various embodiments may also includediagnostics to inform the driver if the oil lubrication system orcooling system (which may cool the traction battery, electric drivetrain, DC/DC converter, e-drive electronics, etc. to provide systemoperation as described herein) is unavailable due to an inoperable pump,LV system, or HV system and provide an alert via a linked wirelessdevice or vehicle components such as flashing lights, horn, siren, etc.The towed electrified vehicle may provide automatic regenerative and/orfriction braking to eliminate the need for a brake pedal pusher, usingacceleration/deceleration of the towed vehicle in place of or inaddition to a braking signal from the towing vehicle.

In addition, various embodiments provide the ability for the driver tospecify a target charge as a target energy (e.g. in watt-hours),percentage SOC or DTE for the towed electrified vehicle upon arrival atthe destination with the control system calculating the charge neededduring the trip and making adjustments as needed to help reach thetarget by the end of the trip. The calculation of charge is net into theHV traction battery, not delivered from the wheels, such that anyvehicle loads while towing do not affect the level of charging, as longas regeneration limits are not reached. The ability to achieve thedesired state of charge while collecting as much active braking energyas possible by distributing the charge throughout the trip instead ofcapturing the energy at a maximum rate at the beginning of the trip mayprovide better drivability for the towing vehicle while reducing theeffect of battery charging during towing on the drivability, coolingsystem, and propulsion system of the towing vehicle allowing the towingvehicle to operate at a more efficient operating point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a towed electrified vehicle having control featuresactivated for towed vehicle operation according to one or moreembodiments.

FIG. 1B illustrates a representative electrified vehicle having acontroller configured to control various vehicle systems during towedvehicle operation.

FIG. 1C illustrates representative electrified vehicle sensors,components, driver assistance features and related systems that may beenabled, disabled, or otherwise controlled while a towed vehicle mode isactive.

FIGS. 2-3 are block diagrams illustrating operation of a system ormethod for controlling a towed electrified vehicle including activationof a towed vehicle mode via a vehicle human-machine interface (HMI).

FIG. 4 is a block diagram illustrating operation of a system or methodthat controls the braking system for active braking or regenerativeenergy capture for traction battery charging in an electrified vehiclewhile towed vehicle operation is enabled.

FIGS. 5-6 are block diagrams illustrating operation of a system ormethod that controls non-braking regenerative energy capture to achieveor maintain a battery target state of charge (SOC) in an electrifiedvehicle while being towed.

FIG. 7 is a block diagram illustrating operation of a system or methodthat uses a desired range or distance to empty (DTE) to control batterycharging in an electrified vehicle while being towed.

FIG. 8 is a block diagram illustrating operation of a system or methodthat controls active braking based on vehicle acceleration/decelerationin an electrified vehicle while being towed.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale and may be simplified; somefeatures could be exaggerated, minimized, or omitted to show details ofparticular components. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a representative basis for teaching one skilled in the art tovariously employ the claimed subject matter. As those of ordinary skillin the art will understand, various features illustrated and describedwith reference to any one of the figures can be combined with featuresillustrated in one or more other figures to produce embodiments that arenot explicitly illustrated or described, but within the scope of theclaimed subject matter. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

The present inventors have recognized that electrified vehicles,particularly Battery Electric Vehicles (BEVs), are not designed to beflat towed (i.e. all wheels in contact with the road surface) with theignition off because the transaxle bearings require active lubricationfrom an electric oil pump. In addition, high speed vehicle operationwith electric drive motors can also generate a high ElectroMagneticForce (EMF) voltage that could damage HV components without activemitigation using the motor inverter system controller (power electronicsmodule 126 in FIG. 1 ). As such, flat towing speed and distance of a BEVmay be limited to 35 MPH/50 miles range, for example, to reducepotential bearing wear. While the BEV could be placed in Driving modewhile being towed behind a towing vehicle, this could result in the BEVshifting to Park when the vehicle door is closed, and may require thekey to be left in the vehicle for the vehicle to actively performregenerative braking to maintain or increase the HV battery state ofcharge and support the low-voltage loads. If the vehicle shuts down dueto a fault or timeout, the control system may enter Park or Neutral,which can cause tire wear, parking pawl wear, or transaxle bearing wearif the vehicle is subsequently moved. Finally, towing in Drive mode mayset diagnostic codes and generate alerts or issues with driverassistance features such as lane centering/departure steering and alertsor emergency braking assist, for example, as the towing vehicle may beidentified as a threat requiring active braking or steeringintervention. Similarly, certain diagnostic codes may disable or shutdown the assistance systems, such as a blocked sensor code, for example.There are also cases where a customer may want to tow the vehicle torecharge a completely depleted HV battery, which may not be possiblewith current designs. As such, various embodiments according to thedisclosure solve one or more of these issues and related issues that mayotherwise arise from towing an electrified vehicle while providing oneor more advantages with respect to vehicle operation and performance aswell as operator convenience.

FIG. 1A illustrates a representative embodiment of a system 20 having atowing vehicle 30 coupled to a towed electrified vehicle 112 by a towbar 50. While illustrated as a recreational vehicle, towing vehicle 30may be any type of vehicle and may include a conventional powertrain orbe implemented by an electrified vehicle. Similarly, while illustratedas a passenger car, towed electrified vehicle 112 may be any type ofvehicle with a partially or fully electrified propulsion systemincluding but not limited to a battery electric vehicle (BEV) or plug-inhybrid electric vehicle (PHEV). In some embodiments, tow bar 50 mayinclude a force or strain sensor 52 that detects the relative push/pullforce between the towing vehicle 30 and the towed electrified vehicle112 for use by towed electrified vehicle 112 in controlling automaticbraking, detecting disconnection from the towing vehicle, etc. Tow bar50 may include an associated electrical connection 54 to supply electricpower and/or control signals from towing vehicle 30 to one or morecomponents or systems 62 of towed electrified vehicle 112. As describedin greater detail herein, depending on the particular implementation ofa towed vehicle operating mode according to this disclosure, a wired orwireless connection between the towing vehicle 30 and towed electrifiedvehicle 112 may be optional, or may be required for utilization of some,but not all towed vehicle operations. For example, if both the tractionbattery and auxiliary battery of electrified vehicle 112 are fullydepleted, an electrical connection 52 may provide temporary low-voltagepower to electrified vehicle 112 sufficient to operate a vehicle HMI toactivate the towed vehicle control with temporary limited functionalityof electric components until subsequent power provided by regenerativebraking or other generator operation of the towed electrified vehicle112 is sufficient to power the system and charge the auxiliary batteryand/or traction battery.

While FIG. 1A illustrates electrified vehicle 112 being flat towed bytowing vehicle 30 with all wheels of electrified vehicle 112 in contactwith the road surface, the present disclosure is not limited to flattowing with some or all features described herein available for use byelectrified vehicles towed by a dolly or similar arrangement with onlysome of the towed electrified vehicle wheels in contact with the roadsurface. Those of ordinary skill in the art will recognize variousfeatures described herein that may be unavailable or inoperabledepending on whether one or more wheels of the electrified vehicle incontact with the road surface are coupled to the electrified vehiclepropulsion system including at least one electric machine and energystore. As a non-limiting example, battery charging and regenerativebraking may be unavailable or inoperable when none of the wheels of theelectrified vehicle contacting the road surface are coupled to thepropulsion system.

FIG. 1B illustrates a representative towed electrified vehicle 112implemented by a plug-in hybrid-electric vehicle (PHEV) for purposes ofillustration and description. As previously described, those of ordinaryskill in the art will recognize that towed vehicle operation asdescribed herein may be used in other types of towed electrifiedvehicles, such as a battery electric vehicle (BEV), which do not includean engine 118. Similarly, towed vehicle operation is not limited topassenger vehicles and may include commercial and transportationvehicles as well as other non-vehicle applications.

A plug-in hybrid-electric vehicle 112 may include one or more electricmachines 114 mechanically coupled to a gearbox or hybrid transmission116. The electric machines 114 may be capable of operating as a motorand a generator. In addition, the hybrid transmission 116 ismechanically coupled to an engine 118. The hybrid transmission 116 isalso mechanically coupled to a drive shaft 120 that is mechanicallycoupled to one or more of the wheels 122. While representativeelectrified towed vehicle 112 is illustrated with a front-wheel drivepropulsion system, the claimed subject matter is generally independentof the particular type of propulsion system and may include rear-wheeldrive, all-wheel drive, four-wheel drive, e-drive systems, for example.The electric machines 114 can provide propulsion and regenerativebraking capability when the engine 118 is turned on or off. The electricmachines 114 may also act as generators and can provide fuel economybenefits by recovering energy that would normally be lost as heat in afriction braking system. The electric machines 114 may also reducevehicle emissions by allowing the engine 118 to operate at moreefficient speeds and allowing the hybrid-electric vehicle 112 to beoperated in electric mode with the engine 118 off under certainconditions. An electrified vehicle 112 may also be a battery electricvehicle (BEV) without an engine 118.

A battery pack or traction battery 124 stores energy that can be used bythe electric machines 114. The traction battery 124 may provide a highvoltage (HV) direct current (DC) output. As generally understood bythose of ordinary skill in the art, high voltage generally refers tovoltages above 60 VDC and representative traction battery packs mayconnect multiple low-voltage cells to operate at a pack voltage in thehundreds of volts, such as 300-800 VDC, for example. Low voltage (LV)systems and components for passenger vehicles may operate at a nominal12 VDC, while commercial vehicles or transportation vehicles may have LVsystems that operate at 24 VDC or 48 VDC, for example.

Towed electrified vehicle 112 may include a contactor module 142 havingone or more contactors configured to isolate the traction battery 124from a high-voltage bus 152 when opened and connect the traction battery124 to the high-voltage bus 152 when closed. The contactor module 142may disconnect the HV bus 152 at key-off or when the vehicle is in anaccessory (ACC) or other non-propulsion mode. As described herein,activation of a towed vehicle mode may control contactor module 142 tocouple the traction battery 124 to the HV bus 152 to provide LV systemsupport, auxiliary battery charging, traction battery charging, and/orregenerative braking.

Contactor module 142 may include one or more contactors to connect orisolate power conversion module or charger 132 from the high-voltage bus152. The high-voltage bus 152 may include power and return conductorsfor carrying current over the high-voltage bus 152. The contactor module142 may be located in the traction battery 124. One or more powerelectronics modules 126 (also known as an inverter) may be electricallycoupled to the high-voltage bus 152. The power electronics modules 126are also electrically coupled to the electric machines 114 and providethe ability to bi-directionally transfer energy between the tractionbattery 124 and the electric machines 114. For example, a tractionbattery 124 may provide a DC voltage while the electric machines 114 mayoperate with a three-phase alternating current (AC) to function. Thepower electronics module 126 may convert the DC voltage to a three-phaseAC current to operate the electric machines 114. In a regenerative mode,the power electronics module 126 may convert the three-phase AC currentfrom the electric machines 114 acting as generators to the DC voltagecompatible with the traction battery 124.

In addition to providing energy for propulsion, the traction battery 124may provide energy for other vehicle electrical systems. The towedelectrified vehicle 112 may include a DC/DC converter module 128 thatconverts the high voltage DC output from the high-voltage bus 152 to alow-voltage DC level of a low-voltage bus 154 that is compatible withlow-voltage loads 156. As illustrated and described in greater detailwith respect to FIG. 1C, LV loads may include one or more fluid pumpsthat pump a lubricating and/or cooling fluid to the vehicle drivetrainor propulsion system, which may include electric machines 114,transmission 116, engine 118, traction battery 124, DC/DC convertermodule 128, and power conversion module 132, for example. Other LV loadsinclude various system controllers or control modules that power and/orcontrol vehicle accessories, lights, displays, interfaces, driverinputs, etc.

An output of the DC/DC converter module 128 may be electrically coupledto a low-voltage auxiliary battery 130 (i.e., 12V, 24V, or 48V battery)for charging the auxiliary battery 130. The low-voltage loads 156 may beelectrically coupled to the auxiliary battery 130 via the low-voltagebus 154. One or more controllers, such as system controller 148 may bepowered by the low-voltage bus 154. Similarly, various vehicleactuators, including contactor module 142 may have low-voltage controlsignals powered by the low-voltage bus, or by drivers of an associatedcontroller or I/O interface that provide low-voltage control signals.One or more high-voltage electrical loads 146 may be coupled to thehigh-voltage bus 152. The high-voltage electrical loads 146 may have anassociated controller that operates and controls the high-voltageelectrical loads 146 when appropriate. Examples of high-voltageelectrical loads 146 may be a fan, an electric heating element, and/oran air-conditioning compressor.

As generally understood by those of ordinary skill in the art,low-voltage components may have different voltage levels for operation,and different applications or implementations may utilize differentvoltage levels for similar components. Low-voltage generally refers tovoltages less than 60 VDC (or 30 VAC) with some vehicles having anominal 12V system, while others have 24V or 48V systems for poweringconvenience features and controllers. High-voltage generally refers tovoltages greater than 60V and may range up to 1500V DC (or 1000 VAC),for example. Typical high-voltage traction batteries for passengervehicles are in the range of 200-450 VDC while some commercial vehiclesinclude traction batteries operating at 400-800 VDC.

The electrified vehicle 112 may be configured to recharge the tractionbattery 124 from an external power source 136. The external power source136 may be a connection to an electrical outlet. The external powersource 136 may be electrically coupled to a charge station or electricvehicle supply equipment (EVSE) 138. The external power source 136 maybe an electrical power distribution network or grid as provided by anelectric utility company. The EVSE 138 may provide circuitry andcontrols to manage the transfer of energy between the power source 136and the vehicle 112. The external power source 136 may provide DC or ACelectric power to the EVSE 138. The EVSE 138 may have a charge connector140 for coupling to a charge port 134 of the vehicle 112. The chargeport 134 may be any type of port configured to transfer power from theEVSE 138 to the vehicle 112. The charge port 134 may be electricallycoupled to an on-board power conversion module or charger 132. Thecharger 132 may condition the power supplied from the EVSE 138 toprovide the proper voltage and current levels to the traction battery124 and the high-voltage bus 152. The charger 132 may be electricallycoupled to the contactor module 142 as previously described to connectcharger 132 to high voltage bus 152. The charger 132 may interface withthe EVSE 138 to coordinate the delivery of power to the vehicle 112. TheEVSE connector 140 may have pins that mate with corresponding recessesof the charge port 134. Alternatively, various components described asbeing electrically coupled or connected may transfer power using awireless inductive coupling.

Wheel brakes 144 may be provided for slowing the vehicle 112 andpreventing motion of the vehicle 112. The wheel brakes 144 may behydraulically actuated, electrically actuated, or some combinationthereof to actuate friction pads to contact a disc or drum of the wheel.The wheel brakes 144 may be a part of a brake system 150. The brakesystem 150 may include other components to operate the wheel brakes 144.For simplicity, the figure depicts a single connection between the brakesystem 150 and one of the wheel brakes 144. A connection between thebrake system 150 and the other wheel brakes 144 is implied. The brakesystem 150 may include a controller to monitor and coordinate the brakesystem 150. The brake system 150 may monitor the brake components andcontrol the wheel brakes 144. The brake system 150 may respond to drivercommands and may also operate autonomously to implement features such asautomatic emergency braking, anti-lock braking, and stability control.The controller of the brake system 150 may implement a method ofapplying a requested brake force when requested by another controller orsub-function, such as system controller 148. When regenerative brakingis enabled and available, system controller 148 may coordinate brakingforce generated by regenerative braking with the braking force of brakesystem 150 provided by the friction brakes 144. Friction brakes 144 maybe applied to all wheels when a parking brake is activated. Someelectric vehicles may automatically apply or activate the parking brakeafter a predetermined time under specified conditions, such as while thevehicle gear selector is in Drive, the vehicle is on an incline, thebrake pedal is depressed, driver's door is open with the gear selectorin Drive, etc.

As described in greater detail herein, activation of towed vehicleoperation may control brake system 150 including regenerative brakingand/or friction braking to slow or stop the towed electrified vehicle112 under various operating conditions, such as if the towed electricvehicle 112 becomes disconnected from the towing vehicle 30, in responseto braking of the towing vehicle 30, or to charge the traction battery124 and/or auxiliary battery 130. Activation of towed vehicle operationmay also suspend or modify operation of selected automatic brakingfunctions or features to facilitate towed vehicle operation, such assuspending automatic parking brake apply, automatic emergency brakingbased on detection of an object, etc.

The electrified vehicle 112 may further include a human-machineinterface (IMI) or user interface (UI) 160. The user interface 160 mayprovide a variety of display elements for communicating information tothe operator. The user interface 160 may provide a variety of inputelements for receiving information from the operator. The user interface160 may include one or more displays. The displays may be touch-screendisplays that both display information and receive input. The userinterface 160 may include discrete lamps/lights. For example, the lampsmay include light-emitting diodes (LED). The user interface 160 mayinclude switches, rotary knobs, sliders, and buttons for allowing theoperator to change various settings. The user interface 160 may includea control module that communicates via the vehicle network. In variousembodiments, the HMI 160 may be used to select or activate towed vehicleoperation and may be used to select various options within the towedvehicle operation mode, such as whether to enable regenerative braking,whether to charge traction battery 124, a desired state of charge (SOC)or distance to empty (DTE) for traction battery 124, a charging rate fortraction battery 124 (i.e. whether to charge as soon as possible, orspread charging events over anticipated trip time/distance/route), andvarious other selections and settings that may vary by the particularapplication and implementation.

Electronic modules in the vehicle 112 may communicate via one or morevehicle networks. The vehicle network may include a plurality ofchannels for communication. One channel of the vehicle network may be aserial bus such as a Controller Area Network (CAN). One of the channelsof the vehicle network may include an Ethernet network. Additionalchannels of the vehicle network may include wired or wireless discreteconnections between modules and may include power signals from theauxiliary battery 130. Different signals may be transferred overdifferent channels of the vehicle network. For example, video signalsmay be transferred over a high-speed channel (e.g., Ethernet) whilecontrol signals may be transferred over CAN or discrete signals. Thevehicle network may include any hardware and software components thataid in transferring signals and data between modules. The vehiclenetwork is not explicitly shown in FIGS. 1A-1C, but it may be impliedthat the vehicle network may connect to any electronic modules that arepresent in the vehicle 112. A vehicle system controller (VSC) 148 may bepresent to coordinate the operation of the various components.

While illustrated as a single controller, controller 148 generallyrepresents multiple vehicle controllers that receive signals fromassociated sensors and control corresponding actuators. Controllers orcontrol modules may be dedicated to a particular vehicle system,subsystem, or component and may include programmablemicroprocessor-based controllers and microcontrollers that performvarious functions and algorithms based on stored program instructions.Various controllers may communicate over one or more channels of thevehicle network(s).

FIG. 1C illustrates representative electrified vehicle sensors,components, driver assistance features and related features and systemsthat may be enabled, disabled, modified, or otherwise controlled while atowed vehicle mode is active. Towed vehicle system controller(s) 148 maydirectly or indirectly control various vehicle systems, sensors,actuators, etc. when operating in a towed vehicle mode as previouslydescribed. Controller(s) 148 may enable, disable, modify, or otherwisecontrol driver assistance and automatic convenience and similar featuresas represented at 170, system diagnostics, fault detection, and alertsas represented at 190, driver controls and inputs as represented at 200,braking system control as represented at 220, LV system support asrepresented at 230, and HV traction battery charging or depletion asrepresented at 240, for example.

Driver assistance and automatic features 170 may include automaticemergency braking 172 that is otherwise applied in response to detectingan excessive closure rate with respect to a forward object based onvehicle sensors, that may include distance sensors using one or morecamera(s), radar, lidar, and similar sensors or detectors. This featuremay be disabled or control thresholds modified when operating in thetowed vehicle mode to reduce or eliminate inadvertent triggering basedon detecting the towing vehicle or any objects that may fall from or bedeflected by the towing vehicle.

Automatic shifting of the propulsion system to Park as represented at174 is a feature that some electrified vehicles include to limit vehiclemotion and stop the vehicle if an operator exits the vehicle while thepropulsion system is in Neutral, Reverse, or Drive, for example. Thefeature may normally be triggered based on detecting the driver doorbeing opened with the propulsion system in Drive. Automatic parkingbrake apply as represented at 176 is a feature that some electrifiedvehicles include to automatically apply the parking brake under someoperating conditions. For example, if the vehicle is stopped on anincline with the gear selector is in Drive for a predetermined timeperiod, such as several minutes, the parking brake may be automaticallyapplied. Accelerator pedal position based torque control as representedat 178 is a feature that some electrified vehicles include to provideautomatic regenerative braking when the accelerator pedal is released(lift-pedal braking). Similarly, the vehicle may generate acceleratorpedal position-based creep torque when the vehicle gear selector is inDrive, the accelerator pedal is released, and the vehicle speed is belowa predetermined threshold. Lane departure steering and/or alerts asrepresented at 180 is a feature that may provide active steering tocenter the electrified vehicle within a lane, or to keep the vehiclefrom crossing a recognized lane marker without the turn signal/indicatoractive. Parking assist as represented at 182 is a feature that mayprovide visual or audio alerts and/or active steering based on detectingobjects near the vehicle when operating at low speed with the gearselector in Drive or Reverse.

As also illustrated in FIG. 1C, various system faults, diagnostic codes,and/or alerts 190 may be enabled, disabled, or modified when operatingin a towed vehicle mode. For example, external object detection 192,sensor blocked 194, and/or following distance 196 alerts or faults maybe disabled. Other system faults, alerts, or diagnostic codes specificto towed vehicle operation may be enabled, such as faults and alertsrelated to electric pump operation, regenerative braking operation,traction battery or auxiliary battery status, etc.

Towed vehicle operation mode may also control or modify control ofvarious driver controls and inputs as represented at 200. Inputs may bedisabled as a theft deterrent feature that requires the presence of thevehicle key and key off/on cycle to deactivate the towed vehicleoperation mode and reset the vehicle systems. Driver controls and inputsthat may have an altered response, may be disabled, or may be otherwisemodified include inputs from a steering wheel 202, headlights anddaytime running lights (DRL) 204, turn signal indicator 206, cruisecontrol 208, gear selector 210, accelerator 212, and windshield wipers214, etc. As an example, turn signal/indicator 206 may be disabled sothat inadvertent operation when enabling the towed vehicle mode does notcontinue while the vehicle is being towed. The turn signals, taillights, brake lights, and other vehicle exterior lighting may becontrolled based on an electrical signal from the towing vehicle.Alternatively, or in combination, turn indicators may be controlled inresponse to automatic detection of an active turn indicator of thetowing vehicle using one or more vehicle cameras or sensors such that awired or wireless connection to the towing vehicle is not required.Similarly, brake lights may be controlled in response to detectingactive brake lights of the towing vehicle, or in response to applyingfriction brakes of the towed vehicle. Operation of headlights/DRL 204based on ambient lighting or gear selector position may be disabledregardless of the particular setting of the headlight control knob.Accelerator pedal 212 input may be disabled to prevent vehicledrive-away theft. Various other systems or features that may otherwiseunnecessarily use power from the towed vehicle may be disabled, such aswindshield wipers 214, vehicle ambient lighting, infotainmentsystem/speakers, climate control, etc. Depending on the particularapplication and implementation, the towed vehicle operation mode mayprovide various configuration settings or options for the user to selectparticular features to enable/disable and/or select a modified responsefor a particular feature. For example, the system may allow or disableoperation of the vehicle climate control to heat/cool the vehicle cabinwhile being towed and/or specify a minimum battery SOC or DTE foroperation of climate control. Those of ordinary skill in the art mayrecognize numerous other settings or configuration options that may beused to control individual vehicle features or inputs based on therepresentative examples of this disclosure.

The towed vehicle system controller(s) 148 may also enable, disable, ormodify control of various braking system features/functions asrepresented at 220. This may include providing regenerative brakingassist 222, friction braking assist 224, and breakaway braking 226.Regenerative braking assistance as represented at 222 may be provided toslow the electrified vehicle in response to a braking signal from thetowing vehicle, or may be automatically actuated by detectingdeceleration of the towed vehicle using towed vehicle speed sensors oraccelerometer, for example, as described in greater detail herein.Regenerative braking assist may be activated independently fromregenerative braking used to charge the traction battery. Similarly,friction braking assist 224 may be provided in response to a brakingsignal from the towing vehicle, or may be automatically actuated.Breakaway braking 226 detects disconnection of the electrified vehiclefrom the towing vehicle and may be used to bring the towed electrifiedvehicle to a controlled stop and apply the parking brake as described ingreater detail with respect to FIGS. 2-8 . Other braking system controlfunctions may be modified when the vehicle is operating in a towedvehicle mode, such as traction control or stability control, forexample.

Low voltage system support 230 may include control of the HV tractionbattery system 232 to close associated contactors to couple the tractionbattery to the HV bus to operate a coolant pump 234 and/or oil pump 236or to charge the LV auxiliary battery 238. As previously described, thetraction battery may supply power to the LV bus via a DC/DC converter.Depending on the particular system configuration and settings, thetraction battery may be coupled to the HV bus to operate HV or LV loadsas previously described. Similarly, coolant pump 234 and/or oil pump 236may be powered by LV auxiliary battery 238 via the LV bus under variousoperating conditions with LV system support 230 provided by the HVtraction battery 232 to charge the LV auxiliary battery 238 based onassociated operating thresholds or settings for the HV traction battery232 and LV auxiliary battery 238.

Towed vehicle operation mode may also enable, disable, or modify controlof the HV battery charging as represented at 240. As described ingreater detail with respect to FIGS. 2-8 , HV traction battery chargingmay be enabled while the electrified vehicle is being towed usingregenerative braking to achieve or maintain a desired SOC or DTE 242 forthe traction battery. Alternatively, or in combination, the system mayuse regenerative braking to charge the traction battery to a minimum SOCto provide LV system support and various other functionality while thevehicle is being towed regardless of whether the user has activatedtraction battery charging or selected a desired target SOC/DTE 242.

FIGS. 2-8 illustrate operation of a system or method for controlling anelectrified vehicle having a towed vehicle operating mode. Control logicor functions performed by one or more controllers, modules, processors,etc. is generally represented in the diagrams of FIGS. 2-8 . Thisillustration provides a representative control strategy, algorithm,and/or logic that may be implemented using one or more processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various steps or functionsillustrated may be performed in the sequence illustrated, in parallel,or in some cases omitted. Although not always explicitly illustrated,one of ordinary skill in the art will recognize that one or more of theillustrated steps or functions may be repeatedly performed. Similarly,the order of processing is not necessarily required to achieve thefeatures and advantages of the claimed subject matter as describedherein, but is provided for ease of illustration and description. Thecontrol logic may be implemented primarily in software executed by amicroprocessor-based vehicle, engine, electric machine, and/orpowertrain controllers, generally represented by system controller 148of FIG. 1B. Of course, the control logic may be implemented in software,hardware, or a combination of software and hardware in one or morecontrollers depending upon the particular application. When implementedin software, the control logic may be provided in one or morenon-transitory computer-readable storage devices or media having storeddata representing code or instructions executed by a computer to controlthe vehicle or its subsystems. The computer-readable storage devices ormedia may include one or more of a number of known physical deviceswhich utilize solid state, electric, magnetic, and/or optical storage tokeep executable instructions and associated calibration information,operating variables, and the like.

FIGS. 2-3 are block diagrams illustrating operation of a system ormethod for controlling a towed electrified vehicle including activationof a towed vehicle mode via a vehicle human-machine interface (HMI).

As illustrated in FIG. 2 , representative control logic or algorithm 250begins at block 260 with starting the vehicle in Accessory mode with thegear selector in Park. As generally understood by those of ordinaryskill in the art, the Accessory mode powers various vehicle conveniencefeatures using the LV auxiliary battery but does not enable propulsionof the vehicle. In contrast, a Run mode powers the system using the HVtraction battery and enables vehicle propulsion. Activation of aRun/Drive mode often requires depressing the brake pedal while pressinga Start/Ignition button. In one or more embodiments according to thepresent disclosure, the HV traction battery contactor may be closedwhile operating in towed vehicle mode with the ignition in Accessorymode to provide LV system support, regenerative braking, HV tractionbattery charging, and various other system features and functions asdescribed herein. While in Accessory mode, the towed electrified vehicleHMI may display a menu on an associated touchscreen an generate a towedvehicle operation signal in response to an operator selecting therecreational tow mode as represented at 262. As an anti-theft deterrent,once entered, the towed vehicle operation mode cannot be exited withoutan ignition/key power off cycle, which requires presence of the vehiclekey to restart the vehicle and enter propulsion (Drive) mode.

The operator may input a desired target SOC (or DTE) for the tractionbattery as well as a travel distance or duration as represented at 264.Alternatively, travel distance, trip duration and/or route may beentered via the vehicle navigation system, or transferred from a mobiledevice, such as a smartphone, by a wired or wireless connection to theelectrified vehicle. The system then calculates a non-brakingregenerative power estimate to achieve the desired target SOC based onthe travel distance, route, or time as represented at 266 and describedin greater detail with reference to FIGS. 5-6 . The non-brakingregenerative power is used to control the electric machine(s) to operateas generator(s) to charge the traction battery, which may in turn beoperated to charge the LV auxiliary battery in various embodiments.

Block 268 determines whether active charging of the traction battery hasbeen requested via the HMI menu. If Yes, block 270 sets the HV tractionbattery desired target SOC (or DTE as illustrated and described withreference to FIG. 7 ) to an active charge level as selected by the user.If No, block 272 sets the HV traction battery SOC target to the higherof the current SOC or preset minimum SOC. Block 272 will charge the HVtraction battery to the minimum SOC or maintain the current SOC whilebeing towed. Block 274 displays a towed vehicle mode message on thevehicle HMI with a reminder to verify that the towed vehicle is properlycoupled to the towing vehicle and that the vehicle must be placed inDrive gear after starting the vehicle as represented at 276. Block 290provides a non-braking regenerative energy capture for HV tractionbattery charging as illustrated and described with reference to FIG. 4 .

Block 278 determines whether the gear selector is in Drive. If No,control continues to block 380 of FIG. 3 . If Yes, block 280 disablesone or more driver assistance or convenience features that areundesirable in towed vehicle operation mode. In the representativeexample of FIG. 2 , block 280 disables automatic return to Park, whichmay otherwise shift the vehicle into Park upon detecting that the driverdoor is open with the vehicle at low speed and in Drive. Block 282disables one or more driver inputs/controls as previously described,which may include the accelerator pedal, cruise control, headlight modeselector, etc. Brake pedal control remains active to allow use of acommercially available third-party brake pedal pusher in the towedvehicle if desired. Block 284 displays via the HMI that the towedvehicle mode is fully active and control continues with block 310 ofFIG. 3 .

Block 310 of FIG. 3 determines whether the HV traction battery isdepleted to below a minimum SOC where the vehicle would not be drivablewithout being towed, but has sufficient power to close the HV tractionbattery contactors so that the traction battery is coupled to the HVbus. Block 310 also determines whether the vehicle speed is below aspeed threshold, such as 10 kph. If Yes, the towed electrified vehiclewill attempt to conserve power by keeping the electric pumps off asrepresented at 312 until the traction battery reaches the minimum SOC orthe vehicle speed exceeds the speed threshold where regenerative powercapture is sufficient to charge the traction battery and/or operate theelectric pumps as previously described. If No at block 310, then theelectric pumps are enabled for operation as represented at 314. Afterbeing enabled, the pumps may be controlled to operate continuously orintermittently in response to corresponding operating criteria, such ascooling system temperature, vehicle speed, elapsed time, etc. tomaximize system efficiency.

Block 316 monitors operation of the lubrication system including thelubrication pump, which may include monitoring pressure, flow,temperature, or other feedback signals, for example. If no lubricationfault is detected, block 318 monitors the propulsion system for properoperation. Propulsion system monitoring may detect the HV batterycontactor opening, a DC/DC converter fault, electric machine fault,electric isolation fault, or HV battery depleted below a shutdownthreshold, for example. If a lubrication fault is detected at 316 or apropulsion system fault is detected at 318, then block 320 generates acorresponding alert and may store one or more corresponding diagnosticcodes. The corresponding alert(s) may be transmitted to a mobile devicevia a wired or wireless connection between the towed electric vehicleand the towing vehicle to alert the driver of the towing vehicle. As anon-limiting illustrative example, alerts may be communicated viacellular, Bluetooth, Wi-Fi, or similar wireless technologies to asmartphone app with a push notification to alert the driver.Alternatively, a wired connection between the towed vehicle and thetowing vehicle may generate a prompt on the towing vehicle HMI, orilluminate a dedicated LED, for example. In one or more embodiments,alerts may include an intermittent horn beep with a predeterminedpattern, flashing lights, and/or headlights flashing, for example.

In response to the lubrication and/or propulsion system fault, block 322may automatically shift the propulsion system from Drive to Neutralwhile inhibiting any other fault responses that may otherwise shift thetowed vehicle to Park or apply the parking brake to reduce or eliminateundesirable wear to various propulsion system components. The propulsionsystem is then shut down, the HV traction battery contactor is opened todisconnect the traction battery from the HV bus, and the electric oiland water pumps are turned Off as indicated at 324. After apredetermined time, such as five minutes for example, the ignitionsystem is automatically commanded Off with the vehicle remaining inNeutral as represented at 326 to preserve the LV auxiliary batterycharge and the towed vehicle operating mode is exited as indicated at330.

If neither block 316 nor block 318 detect a fault, then block 340monitors vehicle speed of the towed electrified vehicle to determinewhether the vehicle is stationary based on vehicle speed being below anassociated threshold for a predetermined period of time, such as beingbelow 1 kph for 2 hours, for example. If Yes, block 350 may alert theuser via a wired or wireless alert and/or using one or more vehicleaudible or visual notifications similar to those previously describedwith respect to block 320. This alert reminds the user that the towedvehicle has been stationary while the towed vehicle operation mode isactive to reduce the possibility for unintended depletion of the LVauxiliary battery and/or the HV traction battery. If No, or aftersending notification to the user, block 360 determines whether thevehicle remains in Drive. If the vehicle is no longer in Drive mode,then block 370 may override the gear selection and shift to Neutral,unless Park is selected, in which case the vehicle will remain in Park.

Block 380 determines whether the ignition has been switched to Off andif Yes, exits the towed vehicle operation mode as represented at 330.Otherwise, control continues with block 410 of FIG. 4 as represented at390.

FIG. 4 is a block diagram illustrating operation of a system or methodthat controls the braking system for active braking or regenerativeenergy capture for traction battery charging in an electrified vehiclewhile towed vehicle operation is enabled. System or method 400determines whether an active braking signal or condition has beendetected as represented at 410. The active braking signal may bedetected in response to depressing of the vehicle brake pedal by acommercially available brake pedal pusher installed in the vehicle.Alternatively, or in combination, the towed vehicle may receive abraking signal from a wired connection to the towing vehicle, or mayautomatically engage active braking in response to vehicle decelerationexceeding a threshold. Towed vehicle deceleration may be determined bymonitoring towed vehicle speed and/or from one or more accelerometers,for example. If yes, block 420 may engage regenerative braking and/orfriction braking to meet the active braking demand, with regenerativebraking subject to traction battery SOC and charge rate/current limits.The towed vehicle brake lights may also be activated based on a signalfrom the towing vehicle, an active braking request exceeding acorresponding threshold, or a towed vehicle deceleration exceeding acorresponding threshold, for example. Control then continues to block290 of FIG. 2 as represented at 480.

If an active braking request is not detected at 410, then the systemcontinues to determine whether operating conditions are favorable forregenerative energy capture to charge the traction battery as generallyrepresented by blocks 430-480. In the representative embodimentillustrated, block 430 determines whether the towed vehicle is above aminimum regenerative energy recapture threshold. If Yes, block 440determines whether the towed vehicle acceleration is below acorresponding threshold, and block 450 determines whether the detectedroad grade is below a corresponding threshold so that regenerativeenergy capture does not adversely affect the ability of the towingvehicle to accelerate or maintain speed while ascending a grade. If theconditions of blocks 430, 440, and 450 are satisfied, then regenerativeenergy capture is engaged as indicated at 460 with the rate of capturedetermined as illustrated and described in greater detail with respectto FIG. 5 . If any of the conditions of blocks 430, 440, or 450 is notsatisfied, then the regenerative energy capture is suspended ordisengaged as represented at 432. Control then continues to block 290 ofFIG. 2 as represented at 480.

FIGS. 5-6 are block diagrams illustrating operation of a system ormethod that controls non-braking regenerative energy capture to achieveor maintain a battery target state of charge (SOC) in an electrifiedvehicle while being towed. As shown in FIG. 5 , system or method 500determines whether the HV traction battery SOC is below an associatedminimum low threshold for vehicle operation. If Yes, then blocks 512,514, and 516 set associated respective thresholds for minimum vehiclespeed, maximum vehicle acceleration, and maximum grade to enable HVtraction battery charging to different, lower thresholds relative to therespective thresholds of blocks 520, 522, and 524, which are set whenthe HV traction battery SOC is above the minimum low threshold asdetermined at block 510. In the representative embodiment illustrated,block 512 sets the vehicle minimum speed to 1 kph, block 514 sets thevehicle maximum acceleration to zero, and block 516 sets the maximumgrade to zero so that regenerative energy capture may occur under moreoperating conditions than the thresholds of blocks 520, 522, and 524 tocharge the HV traction battery to the minimum low threshold for vehicleoperation. In the representative embodiment illustrated, block 520 setsthe vehicle minimum speed to 10 kph, block 522 sets the vehicle maximumacceleration to 0.5 m/s², and block 524 sets the maximum grade to 2%. Ofcourse, thresholds may vary depending on the particular electrifiedvehicle configuration and desired performance specifications for variousvehicle applications and implementations.

Block 530 determines whether the HV traction battery SOC is below thetarget threshold, which may be specified by the user via the HMI or maybe a default target or a target otherwise determined by the vehiclecontroller(s). If No, block 540 determines whether the HV tractionbattery SOC is above the target threshold. If Yes, block 542 sets thenon-braking regenerative energy capture maximum power limit to anegative value to discharge the HV traction battery to a calibratablelevel, such as −2 kW in this example. Otherwise, the non-brakingregenerative energy capture maximum limit is set to zero (to providezero net current to the traction battery) as represented at 544. Itshould be noted that regenerative capability may also be expressed as atorque limit as a function of vehicle speed as power is equivalent totorque multiplied by speed. The corresponding regenerative power limitfrom blocks 542 or 544 is then provided to block 266 of FIG. 2 asrepresented at 560.

If block 530 determines that the HV traction battery SOC is below thetarget SOC, then block 550 determines whether active charging has beenselected via the HMI when entering the towed vehicle operation mode. IfYes, then block 554 sets the non-braking regenerative charging power tothe minimum or lesser of the regenerative charging power and the liftpedal regenerative power limit as described with respect to FIG. 6 .Otherwise, block 552 sets the regenerative power maximum limit to thelift pedal maximum as described with respect to FIG. 6 . Thecorresponding regenerative power limit from blocks 552 or 554 is thenprovided to block 266 of FIG. 2 as represented at 560.

As illustrated by diagram 600 of FIG. 6 , the non-braking regenerativeenergy capture calculates an average speed for the trip as representedat 610. The average speed may have a default minimum value, such as 30mph, for example. The odometer reading at the start of a trip asrepresented at 620 is used in combination with the current odometerreading at 622 and the total trip distance at 624 to calculate the tripdistance remaining at 630. As previously described, the trip distancemay be manually entered via the HMI, entered via a connected mobiledevice, or obtained from the vehicle navigation system if a destinationhas been entered. The remaining trip distance from block 630 and theaverage speed from block 610 is used to calculate the trip timeremaining at 640. The energy needed to achieve the desired target HVtraction battery SOC by the end of the trip is determined at 660 basedon the target HV traction battery SOC at 662, the current HV tractionbattery SOC at 664, and a lookup table or calculation that provides arelationship between SOC and energy as represented at 666. In variousembodiments, the desired target charge for the HV traction battery maybe entered via the HMI in various forms other than SOC, such as adistance to empty (DTE), or in Watt hours, for example. The controllermay convert the entered desired battery charge regardless of theparticular units or format selected by the user to a net energy inputrequired for the traction battery to control regenerative energy captureas illustrated and described with respect to FIG. 7 for converting DTEto SOC. The net energy calculation may use a theoretical or empiricalcorrelation between Watt hours (energy) and SOC (amp hours of capacity)of a given HV traction battery at a specified temperature and batteryage. Those of ordinary skill in the art will appreciate that the claimedsubject matter is generally independent of the manner of specifying adesired traction battery charge via the HMI and may be converted to anet energy input or equivalent parameter to control regenerative energycapture to charge the traction battery while the electrified vehicle isbeing towed. The remaining trip time from block 640 and the energyneeded to charge the traction battery as determined at 660 is used tocalculate the non-braking regenerative energy capture power asrepresented at 650, which is then used to determine the regenerativecharge power into the HV traction battery as previously described withrespect to block 554 of FIG. 5 .

FIG. 7 is a block diagram illustrating operation of a system or methodthat uses a desired range or distance to empty (DTE) to control batterycharging in an electrified vehicle while being towed. Algorithm 700 maybe used to determine a target traction battery SOC for the electrifiedvehicle based on a desired range or DTE entered via the HMI asrepresented at 710. Block 720 calculates the Watt-hours (WH) neededbased on the DTE consumption (WH/mi) as indicated at 722 and the currentDTE as indicated at 724. Block 730 calculates the target HV tractionbattery SOC using a corresponding lookup table to convert SOC to energybased on the current HV traction battery WH available at 732 andaccessing the SOC to energy lookup table at 734. The calculated SOCbased on the entered DTE is then used by the non-braking regenerativecapture strategy as previously described.

FIG. 8 is a block diagram illustrating operation of a system or methodthat controls active braking based on vehicle acceleration/decelerationin an electrified vehicle while being towed. Towed electrified vehiclesusing automatic deceleration detection to provide breakaway brakingshould come to a complete stop if they become disconnected form thetowing vehicle. System or method 800 monitors the electrified vehicledeceleration to detect a potential breakaway situation and will applymore aggressive braking force using regenerative braking and frictionbraking to bring the towed electrified vehicle to a controlled stop.Because a hard stop by the towing vehicle may be difficult todistinguish from a breakaway condition, any subsequent acceleration willallow the towed electrified vehicle to release the brakes and resumenormal towed vehicle functions.

Block 810 determines whether the brake pedal is depressed by a brakepusher installed in the vehicle. If Yes, block 820 applies activebraking torque based on the brake pedal demand. This may includeregenerative braking and friction braking as previously described.Control then returns to block 410 of FIG. 4 as indicated at 830.Otherwise, block 840 calculates a vehicle acceleration/deceleration rateat 840 based on vehicle speed 842 and/or input from one or moreaccelerometers 844. If deceleration exceeds an associated threshold at850, then block 852 calculates an active braking torque using a lookuptable 854 that provides a relationship between braking torque anddeceleration. Control then returns to block 410 of FIG. 4 as indicatedat 830.

If deceleration is below the associated threshold at 850, then block 860determines whether vehicle speed is below a threshold, priordeceleration as represented at 862 was above a threshold, andacceleration is below a threshold. If yes, then block 880 sets theactive braking request to a preset vehicle hold torque and controlcontinues with block 410 of FIG. 4 as indicated at 830. Otherwise, block870 sets the active braking torque to a value based on the estimatedroad grade from block 864 when the vehicle stops and control continueswith block 410 of FIG. 4 as indicated at 830.

As generally represented in at least blocks 860, 862, 864, 870, and 880of FIG. 8 , if the towed electrified vehicle is disconnected from thetowing vehicle, the towed vehicle will begin to decelerate. This willgenerate a braking signal that will add to the deceleration, generatingmore deceleration, and therefore pass the deceleration rate threshold.As the disconnected towed vehicle slows under this hard deceleration,the system commands the friction brakes to a preset vehicle hold torque,achieving the slowing of a vehicle that is disconnected and also keepingthe vehicle at a stop when it comes to a rest. If the disconnection is afalse detection, then the vehicle will begin to accelerate as the towingvehicle accelerates and the braking torque is released. Depending on theparticular application, block 870 may set the predetermined activebraking torque to zero. In other applications, block 870 may provide apredetermined active braking torque less than the predetermined vehiclehold torque of block 880, but greater than zero. The predeterminedbraking torque of block 870 may be selected based on road gradeestimated at block 864 when the vehicle comes to a stop to so that theweight of the towed vehicle does not result in movement of thetowing/towed vehicles on higher grades. The predetermined braking torqueof block 870 may be less than the preset vehicle hold torque of block880 so the vehicle combination can more easily accelerate afterstopping.

As generally illustrated and described above, a system or methodaccording to this disclosure provides a strategy or algorithm thatcalculates the needed HV traction battery charge rate to achieve adesired SOC or DTE at the destination of the towed electric vehiclebased on distance to the destination rather than a fixed high rate ofcharge that would otherwise front-load battery charging to the beginningof the trip. The algorithm uses a user-specified SOC (or DTE) of theelectrified vehicle at the trip destination to control the rate oftraction battery charging over the duration of the trip to reduce theeffect on drivability and load on the towing vehicle at any particularpoint during the trip. The rate of charge may vary as the vehicletravels to account for higher net charging due to energy capture viabraking, or lower net charging due to low speed or zero speed timeperiods where the HV battery is discharging, not charging, or when thetowing vehicle is ascending a grade or accelerating, for example.

The representative embodiments described are not intended to encompassall possible forms within the scope of the claims. The words used in thespecification are words of description rather than limitation, and it isunderstood that various changes can be made consistent with theteachings of the disclosure within the scope of the claimed subjectmatter. As previously described, one or more features of variousembodiments can be combined to form further embodiments that may not beexplicitly described or illustrated. Although embodiments that have beendescribed as providing advantages over other embodiments or prior artimplementations with respect to one or more desired characteristics,those of ordinary skill in the art recognize that one or more featuresor characteristics can be compromised to achieve desired overall systemattributes, which depend on the specific application and implementation.These attributes can include, but are not limited to strength,durability, life cycle, marketability, appearance, packaging, size,serviceability, weight, manufacturability, ease of assembly, etc. Assuch, embodiments described as less desirable than other embodiments orprior art implementations with respect to one or more characteristicsare not outside the scope of the disclosure and can be desirable forparticular applications.

What is claimed is:
 1. An electrified vehicle comprising: a drivetrainincluding an electric machine configured to provide propulsive torque tovehicle wheels; a high-voltage traction battery selectively connected tothe electric machine; and a controller programmed to, after receiving asignal enabling towed vehicle operation of the electrified vehicle, varycharging rate of the high-voltage traction battery while the electrifiedvehicle is being towed over a user-specified distance to a destinationto obtain a user-specified target charge for the high-voltage tractionbattery upon reaching the destination.
 2. The electrified vehicle ofclaim 1 further comprising a human-machine interface (HMI) incommunication with the controller, wherein the HMI receives theuser-specified distance and the user-specified target charge for thehigh-voltage traction battery, and generates a signal to controlcharging of the high voltage traction battery during towing of theelectrified vehicle in response to associated input.
 3. The electrifiedvehicle of claim 2 wherein the user-specified target charge comprises apercentage state of charge (SOC) of the high-voltage traction battery.4. The electrified vehicle of claim 3 wherein the controller is furtherprogrammed to vary the charging rate based on net energy input to thehigh-voltage traction battery needed to obtain the user-specified targetSOC.
 5. The electrified vehicle of claim 4 wherein the controller variesthe charging rate by varying power generated by the electric machinebased on the net energy needed to obtain the user-specified target SOC.6. The electrified vehicle of claim 5 wherein the controller variespower generated by the electric machine based on a distance remaining tothe destination divided by an average vehicle speed and a differencebetween the target SOC and a current SOC of the high-voltage tractionbattery.
 7. The electrified vehicle of claim 2 wherein theuser-specified target charge comprises a distance to empty (DTE) for theelectrified vehicle and wherein the controller is further programmed toconvert the DTE to a corresponding SOC.
 8. The electrified vehicle ofclaim 7 wherein the controller is further programmed to convert the DTEto the corresponding SOC by retrieving the corresponding SOC from alookup table based on net energy input to the high-voltage tractionbattery needed to obtain the DTE.
 9. The electrified vehicle of claim 8wherein the controller is further programmed to vary the charging rateby controlling non-braking regenerative power of the electric machine.10. A method for controlling an electrified vehicle having a drivetrainincluding an electric machine configured to provide propulsive torque tovehicle wheels and a traction battery, comprising, by a vehiclecontroller: receiving a signal to activate towed vehicle operation; andcontrolling charging rate of the traction battery while the electrifiedvehicle is being towed to distribute charging of the traction battery toa user-specified charge over a user-specified distance.
 11. The methodof claim 10 further comprising receiving the user-specified charge andthe user-specified distance via a human-machine interface (HMI) of theelectrified vehicle after receiving input to activate the towed vehicleoperation from the HMI.
 12. The method of claim 11 wherein theuser-specified charge comprises a percentage state of charge (SOC) ofthe traction battery after traveling the user-specified distance. 13.The method of claim 11 wherein the user-specified charge comprises adistance to empty (DTE) for the electrified vehicle, the method furthercomprising converting the DTE to a corresponding SOC.
 14. The method ofclaim 13 wherein converting the DTE to a corresponding SOC comprisesretrieving the corresponding SOC from a lookup table based on net energyrequired to obtain the DTE.
 15. The method of claim 10 whereincontrolling the charging rate comprises: charging the traction batterybased on a net energy input required to achieve the user-specifiedcharge, the net energy input required being divided by time required totravel the user-specified distance.
 16. The method of claim 15 furthercomprising controlling non-braking regenerative power of the electricmachine to control the charging rate.
 17. An electrified vehicle systemcomprising: a drivetrain including an electric machine powered by atraction battery; a human-machine interface (HMI); and a controllerprogrammed to, in response to an enabling signal received in response toinput via the HMI, control charging rate of the traction battery toevenly distribute charging to a target charge input via the HMI over adistance input via the HMI.
 18. The electrified vehicle system of claim17 wherein the target charge corresponds to a percentage state of charge(SOC) of the traction battery.
 19. The electrified vehicle system ofclaim 18 wherein the target charge is input as a distance to empty (DTE)to the HMI.
 20. The electrified vehicle system of claim 18 wherein thecontroller is further programmed to control regenerative energy captureof the electric machine while being towed to control the charging ratebased on net energy input to the traction battery required to obtain thetarget charge after being towed the distance input via the HMI.